Bump bonded cryogenic chip carrier

ABSTRACT

A technique relates to a device. First thin films are characterized by having a first opposing surface and a first connection surface in which the first connection surface is in physical contact with a first superconducting region. Second thin films are characterized by having a second opposing surface and a second connection surface in which the first and second opposing surfaces are opposite one another. The second connection surface is in physical contact with a second superconducting region. A solder material electrically connects the first and second opposing surfaces, and the solder material is characterized by maintaining a low ohmic electrical contact between the first and second opposing surfaces at temperatures below 100 degrees Kelvin. The first and second superconducting regions are formed of materials that have a melting point of at least 700 degrees Celsius.

BACKGROUND

The present invention relates in general to connecting electricalsignals into and out of a circuit. More specifically, the presentinvention relates to systems, methodologies and resulting bump-bondedinterfaces configured to execute the direct transfer of electronicsignals into and out of cryogenic electronics in a manner thateliminates the need for intermediary electrical connection mechanismssuch as wire bond connections, and the like.

Electronic components may be connected together through differenttechniques. One such method is through wire bonding. Wire bonding is awell-known technique for forming electrical interconnections between anelectronic component (e.g., a printed circuit board (PCB), a packaged orunpackaged integrated circuit (IC), etc.) and other components (e.g.,external components, card sockets, microwave connectors, chip carriers,etc.). In wire bonding, a length of small diameter soft metal wire(e.g., gold (Au), copper (Cu), silver (Ag), aluminum (Al), and the like)is attached or bonded without the use of solder to a compatible metallicsurface or pad mounted on a PCB or an IC/chip carrying substrate. Theactual bond between the wire and the pad can be formed in a variety ofways, including the use of thermo-compression, thermo-sonic andultrasonic techniques.

Components such as IC/chip carriers can be designed to reliably operateunder a variety of conditions, including, for example, cryogenicconditions. The term “cryogenics” refers generally to the branches ofphysics and engineering that involve the study of very low temperatures,how to produce them, and how materials behave at those temperatures. Theterm “reliability” is used in electronics to describe the probabilitythat a component operating under specified conditions will performsatisfactorily for a given period of time. Although wire bonding iswidely used in the fabrication of electronic systems, the additionalwire bond hardware, particularly in cryogenic electronic applications,is manually intensive to fabricate, suffers from low temperature CTE(coefficient of thermal expansion) mismatches, is difficult to reliablyrepeat, causes signal path problems, increases costs, adds bulk and inthe case of microwave/radio frequency (RF) introduces extraneousmicrowave cavity modes.

SUMMARY

Embodiments of the invention are directed a device. Non-limitingexamples of the device include a first plurality of thin films, thefirst plurality of thin films characterized by having a first opposingsurface and a first connection surface, wherein the first connectionsurface is in physical contact with a first superconducting region. Thedevice includes a second plurality of thin films, the second pluralityof thin films characterized by having a second opposing surface and asecond connection surface, the first and second opposing surfaces beingopposite one another, wherein the second connection surface is inphysical contact with a second superconducting region. Also, the deviceincludes a solder material electrically connecting the first and secondopposing surfaces, the solder material characterized by maintaining alow ohmic electrical contact between the first and second opposingsurfaces at temperatures below 100 degrees Kelvin, wherein the first andsecond superconducting regions are comprised of materials that have amelting point of at least 700 degrees Celsius.

Embodiments of the invention are directed a device. Non-limitingexamples of the device include a first plurality of thin films inphysical contact with a first substrate at a first superconductingregion, the first plurality of thin films characterized by having afirst opposing surface and a first connection surface, wherein the firstconnection surface is in the physical contact with the firstsuperconducting region. The device includes a second plurality of thinfilms in physical contact with a second substrate at a secondsuperconducting region, the second plurality of thin films characterizedby having a second opposing surface and a second connection surface, thefirst and second opposing surfaces being opposite one another, whereinthe second connection surface is in the physical contact with the secondsuperconducting region. Also, the device includes a solder materialelectrically connecting the first and second opposing surfaces, thesolder material characterized by maintaining a low ohmic electricalcontact between the first and second opposing surfaces at temperaturesbelow 100 degrees Kelvin, wherein the first and second superconductingregions are comprised of materials that have a melting point of at least700 degrees Celsius.

Embodiments of the invention are directed to a system. Non-limitingexamples of the system include a cooling system and a device in thecooling system. The device includes a first plurality of thin films, thefirst plurality of thin films characterized by having a first opposingsurface and a first connection surface, wherein the first connectionsurface is in physical contact with a first superconducting region. Thedevice includes a second plurality of thin films, the second pluralityof thin films characterized by having a second opposing surface and asecond connection surface, the first and second opposing surfaces beingopposite one another, wherein the second connection surface is inphysical contact with a second superconducting region. Also, the deviceincludes a solder material electrically connecting the first and secondopposing surfaces, the solder material characterized by maintaining alow ohmic electrical contact between the first and second opposingsurfaces at temperatures below 100 degrees Kelvin, wherein the first andsecond superconducting regions are comprised of materials that have amelting point of at least 700 degrees Celsius.

Embodiments of the invention are directed to a method of configuring adevice. Non-limiting examples of the method include forming a firstplurality of thin films, the first plurality of thin films characterizedby having a first opposing surface and a first connection surface,wherein the first connection surface is in physical contact with a firstsuperconducting region. The method includes forming second plurality ofthin films, the second plurality of thin films characterized by having asecond opposing surface and a second connection surface, the first andsecond opposing surfaces being opposite one another, wherein the secondconnection surface is in physical contact with a second superconductingregion. Also, the method includes joining the first and second opposingsurfaces with a solder material such that the solder materialelectrically connects the first and second opposing surfaces, the soldermaterial characterized by maintaining a low ohmic electrical contactbetween the first and second opposing surfaces at temperatures below 100degrees Kelvin, wherein the first and second superconducting regions arecomprised of materials that have a melting point of at least 700 degreesCelsius.

Additional features and advantages are realized through the techniquesdescribed herein. Other embodiments and aspects are described in detailherein. For a better understanding, refer to the description and to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the present invention isparticularly pointed out and distinctly claimed in the claims at theconclusion of the specification. The foregoing and other features andadvantages are apparent from the following detailed description taken inconjunction with the accompanying drawings in which:

FIG. 1A depicts a cross-sectional view of a bump-bonded cryogenicelectronic carrier having microwave connectors according to embodimentsof the invention;

FIG. 1B depicts a cross-sectional view of a bump-bonded cryogenicelectronic carrier having microwave connectors according to embodimentsof the invention;

FIG. 2 depicts an enlarged view of a portion of the cryogenic electroniccarrier according to embodiments of the invention;

FIG. 3 depicts an enlarged view of a portion of the cryogenic electroniccarrier according to embodiments of the invention;

FIG. 4 is a flow chart of a method of forming a bump-bonded deviceaccording to embodiments of the invention;

FIG. 5 depicts a flow chart of a method of forming a device according toembodiments of the invention; and

FIG. 6 depicts a system according to embodiments of the invention.

In the accompanying figures and following detailed description of thedisclosed embodiments, the various elements illustrated in the figuresare provided with three or four digit reference numbers. The leftmostdigit(s) of each reference number corresponds to the figure in which itselement is first illustrated.

DETAILED DESCRIPTION

It is understood in advance that, although this detailed descriptionincludes a description of attaching a specific type of electronicconnector and interconnect structure on a substrate, implementation ofthe teachings recited herein are not necessarily limited to a particulartype of connector, transmission architecture, circuit, or substrate.Rather embodiments of the present invention are capable of beingimplemented in conjunction with any other type of connector,transmission architecture, circuit, or substrate now known or laterdeveloped.

Various embodiments of the present invention are described herein withreference to the related drawings. Alternative embodiments can bedevised without departing from the scope of this invention. It is notedthat various connections and positional relationships (e.g., over,below, adjacent, etc.) are set forth between elements in the followingdescription and in the drawings. These connections and/or positionalrelationships, unless specified otherwise, can be direct or indirect,and the described embodiments of the present invention are not intendedto be limiting in this respect. Accordingly, a connection of entitiescan refer to either a direct or an indirect connection, and a positionalrelationship between entities can be a direct or indirect positionalrelationship. As an example of an indirect positional relationship,references in the detailed description to forming layer “A” over layer“B” include situations in which one or more intermediate layers (e.g.,layer “C”) is between layer “A” and layer “B” as long as the relevantcharacteristics and functionalities of layer “A” and layer “B” are notsubstantially changed by the intermediate layer(s).

Spatially relative terms, e.g., “beneath,” “below,” “lower,” “above,”“upper,” and the like, can be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” can encompass both an orientation ofabove and below. The device can be otherwise oriented (i.e., rotated 90degrees or at other orientations), and the spatially relativedescriptors used herein should be interpreted accordingly.

For the sake of brevity, conventional techniques related to electronicdevice and IC fabrication may or may not be described in detail herein.Moreover, the various tasks and process steps described herein can beincorporated into a more comprehensive procedure or process havingadditional steps or functionality not described in detail herein. Inparticular, various steps in the manufacture of electronic devices andICs are well known and so, in the interest of brevity, many conventionalsteps will only be mentioned briefly herein or will be omitted entirelywithout providing the well-known process details.

Turning now to an overview of aspects of the present invention,embodiments of the invention provide systems that can be used in variousapplications, such as in cryogenic electronics. In embodiments of theinvention, a merged fabrication process is used to form two differenttypes of electrical connections onto a first substrate. The firstsubstrate may be comprised of just a carrier material. Examples ofcarrier materials can include ceramics, silicones, plastics,semiconductors, insulators, polymers, glass, metamaterials, composites,biomaterials, metals, PCB materials, and the like. The first substratemay or may not also include electronic circuitry. The electroniccircuitry may either be fabricated on the surface of the carriermaterial, may be fabricated or integrated within the carrier material,or may be bonded to the carrier material. Examples of electricalcomponents can include: capacitors, inductors, resistors, resonators,filters, lumped element systems, waveguides, Josephson junctions, groundplanes, diodes, transistors, etc. In some embodiments of the invention,two different types of electrical connections are described. Theseelectrical connections include connections to electronic connectors andconnections to a second substrate through bump bonds. In anotherembodiment of the invention, a merged fabrication process that attachesthe above two different types of connections through an interconnectstructure is described. The interconnect structure can be a conductivematerial formed on the first substrate. The electronic connectors andthe bump bonds connect to the interconnect substructure.

The bump bonds are formed from a low temperature solder material andprovided with a size and/or shape that enables an electrical connectionto be made at the point of contact. Examples of a low temperature soldermaterial include: indium, indium tin alloys, indium bismuth alloys,SnAgCu alloy (also referred to as SAC), indium-bismuth-tin, lead-basedsolders (such as, for example, PbSn), etc.

The bump bond may be utilized to mechanically and electrically connectan electronic connector to the first substrate. Examples of electronicconnectors can include any conventional or fabricated surface mountedconnector configured to pass a range of electrical signals, such asdirect current (DC) signals and/or radio frequency (RF) signals (i.e.low frequency RF signals, microwave signals, etc.).

The bump bonds may be utilized to mechanically and electrically connectthe first substrate to a second substrate. The second substrate may becomprised of just a carrier material. Examples of carrier materials caninclude ceramics, silicones, plastics, semiconductors, insulators,polymers, glass, metamaterials, composites, biomaterials, metals, PCBmaterials, and the like. The second substrate may or may not alsoinclude electronic circuitry. The electronic circuitry may either befabricated on the surface of the carrier material, may be fabricated orintegrated within the carrier material, or may be bonded to the carriermaterial. Examples of electrical components can include: capacitors,inductors, resistors, resonators, filters, lumped element systems,waveguides, Josephson junctions, ground planes, diodes, transistors,etc.

The bump bonds, used to connect both the electronic connector to thefirst substrate and connect the first and second substrates together,may be formed simultaneously. By using the same solder material (havingthe same melting point) to form the bumps bonds for connecting theelectronic connectors and connecting the first and second substrates,the need for a solder hierarchy is avoided. Solder hierarchies applymultiple different soldering methodologies tailored to the meltingpoints and other characteristics of the different types of solder underuse. By avoiding solder hierarchies, all solder bonds may be formed atthe same time (i.e., simultaneous soldering).

In embodiments of the invention, a first under-bump-metallization (UBM)structure can be utilized to connect to a first interconnect structureon the first substrate and a second UBM structure can be utilized toconnect to a second interconnect structure on the second substrate. Thefirst UBM structure can include a first stack of materials and thesecond UBM structure can include a second stack of materials. In someembodiments of the invention, the first stack of materials and thesecond stack of materials can be the same. In other embodiments of theinvention, the first stack of materials and the second stack ofmaterials can be different. Furthermore, some layers in the first andsecond stacks may be comprised of different materials and some may becomprised of the same materials.

The interconnect structure (or interconnect layer) can take a variety offorms, including, for example, metal on film, damascene metal, diffusionor any other type of conductive contact area on the first substrate. Theinterconnect structure may either comprise a physically contiguousstructure on the surface of the substrate or may comprise severalstructures that are physically separate from one another on the surfaceof the substrate. Additionally, portions of the interconnect structuremay also be located within the substrate. The first UBM structure andsolder attachment methodology may be utilized to physically secure andelectrically connect an electronic connector directly to the firstinterconnect structure on the first substrate. The material propertiesof the first stack of materials in the first UBM structure are tailoredto the specific joining method and material of the bump bond and theinterconnect structure. In embodiments of the invention, the firstinterconnect structure on the first substrate can electrically connectthe electronic connector to electronic circuitry on the first substrateand/or on the second substrate. Accordingly, embodiments of the presentinvention avoid the manually intensive fabrication, low temperature CTEmismatches, lack of repeatability, signal path problems, increased cost,added bulk and extraneous microwave cavity modes introduced by routingelectronic signals through intermediary connection mechanisms such asPCBs and wire bond connections.

In some embodiments of the invention, the second interconnect structureon the second substrate is electrically and/or physically connected tothe first substrate (e.g., through the first interconnect structure onthe first substrate) through the bump bonds and the second UBM structureusing flip chip fabrication. The above-described “merged” fabricationprocess for forming two different types of electrical connections (i.e.,surface mounted connectors and bonding together of the first and secondsubstrates) on the first substrate can utilize a modified version offlip chip fabrication. To bond the second substrate through the bumpbond, more traditional flip chip fabrication can be used. Accordingly,electrical connections are provided through the electronic connector,the first interconnect structure on the first substrate, the first UBMstructure on the first interconnect structure, the bump bonds, thesecond UBM structure on the second interconnect structure, and thesecond interconnect structure on the second substrate.

In some embodiments, the bump bonds not only provide the electricalconnection between the first and second substrates, the bump bonds alsoprovide thermal conduction through the first and second substrates, andact as spacers to prevent electrical shorts and provide mechanicalsupport. The bump bonds also avoid wire bonding and therefore are ableto be much smaller than their counterparts. The thickness of the metalfilms that form the UBM stack of materials (e.g., first and second UBMstructures) can be thin films, and therefore can be selected to besufficiently thin (e.g., under 3 micrometers (μm) each) such that themetal films become superconducting because they are in sufficientproximity to the bump bonds. In addition, the bump bonds can be formedfrom superconducting materials such as, for example: indium, indium tinalloys, indium bismuth alloys, SnAgCu alloy (also referred to as SAC),indium-bismuth-tin, lead-based solders (such as, for example, PbSn),etc. In this way, a superconducting connection can be formed between theinterconnect structures on the first and second substrates. The size(e.g., diameter) of the bumps can be selected to be sufficiently largeto allow greater than 50 micrometers of spacing between the firstsubstrate (i.e., the interposer) and the second substrate in order tominimize capacitive loading effects between the first and secondsubstrates.

Embodiments of the invention are to be utilized to electrically andmechanically bond electronic components to substrates and/orinterconnect structures using a first UBM structure and a second UBMstructure. Embodiments of the inventions may be described as being usedwith a chip carrier for explanation purposes. It should be appreciatedthat embodiments of the invention are not limited to use with a chipcarrier.

Turning now to a more detailed description of aspects of the invention,FIG. 1A depicts a cross-sectional view of a chip carrier 100 that housesa bump-bonded cryogenic electronic device. The chip carrier 100 caninclude a bottom housing 102, a top housing 104, a first substrate 110,a second substrate 120, and one or more electronic connectors 130 all ofwhich are configured and arranged as shown in FIG. 1A. In embodiments ofthe invention, the first substrate 110 is in a first cavity 103 of thebottom housing 102. In some embodiments of the invention, the secondsubstrate is in a second cavity 105 of the top housing 104. In someembodiments of the invention, the first substrate 110 is not in thebottom housing 102, and/or the second substrate 120 is not in the tophousing 104. In some embodiments of the invention, there is no bottomhousing 102 and/or top housing 104.

In embodiments of the invention, the bottom housing 102 and the tophousing 104 can be formed from copper (Cu). In some embodiments of theinvention, the bottom housing 102 and top housing 104 can be formed ofsome other suitable materials, such as a thermally conductive materialor an insulating crystal. In embodiments of the invention, the bottomhousing 102 and the top housing 104 are physically coupled together byscrews 140. It is noted that the screws 140 are positioned at the edgesof the top and bottom housings 104, 102 such that the screws 140 extendthrough the top and bottom housings 104, 102 but do not extend throughthe first substrate 110. In forming the embodiments of the inventionshown in FIG. 1A, the screws should not be tightened so much that thetoo much pressure is applied to the bumps 122, which can result in thebumps 122 being deformed, which can degrade signal performance. In someembodiments, there are no screws 140 that are used in assembly 100.

The second substrate 120 can be electrically and/or physically connectedto the first substrate 110 through bump bonds 122 havingunder-bump-metallurgy (e.g., UBM structures 220 and 230 shown in FIG.2). For ease of illustration, only one of the four bump bonds 122 shownin FIG. 1A is provided with a reference number. In embodiments of theinvention, the bump bonds 122 are formed from low temperature solder.The low temperature solder are solders that are processed attemperatures below 300 degrees Celsius. The low temperature solder ofthe bump bonds 122 are superconducting materials. Examples of thesuperconducting materials for the low temperature solder can includeindium, indium tin alloy, indium bismuth alloy, SnAgCu alloy (alsoreferred to as SAC), indium-bismuth-tin, lead-based solders (such as,for example, PbSn), etc. Particularly, in one implementation, the lowtemperature solder is indium or indium based.

The electronic connectors 130 can be electrically and physicallyconnected to the first substrate 110 through bump bonds 122. The UBMstructure 220 can be utilized to connect the electronic connectors 130to the first substrate as shown in FIG. 3. In some embodiments of theinvention, the electronic connector 130 is a conventional surfacemounted microwave connector. In other embodiments, the electronicconnector may be one of any conventional or fabricated surface mountedconnector configured to pass a range of electrical signals, such asdirect current (DC) signals and/or radio frequency (RF) signals (i.e.,low frequency RF signals, microwave signals, etc.).

The first substrate 110 and second substrate 120 can be comprised of acarrier material. Examples of carrier materials can include: ceramics,silicones, plastics, semiconductors, insulators, polymers, glass,metamaterials, composites, biomaterials, metals, PCB materials, and thelike. The first substrate 110 and second substrate 120 can also includeelectronic circuitry. The electronic circuitry may either be fabricatedon the surface of the carrier material, may be fabricated or integratedwithin the carrier material, or may be bonded to the carrier material.Examples of electrical components can include: capacitors, inductors,resistors, resonators, filters, lumped element systems, waveguides,Josephson junctions, ground planes, diodes, transistors, etc.

FIG. 1B depicts a cross-sectional view of a chip carrier 170 that housesa bump-bonded cryogenic electronic device according to embodiments ofthe invention. The chip carrier 170 shown in FIG. 1B is substantiallythe same as the chip carrier 100 shown in FIG. 1A except the chipcarrier 170 includes a top housing 174 that extends further laterallythan the top housing 104 shown in FIG. 1A and includes a third cavity106 through which the electronic connectors 130 extend. In FIG. 1B, thetop housing 174 fits against the bottom housing 102 at the edgesthereof, and lateral portions of the top housing 174 are secured to thebottom housing 102 by the screws 140. To avoid the need to carefullyavoid over-tightening the screws 140 to avoid damaging the bumps 122,the dimension of the top housing 174 and the first cavity 105 areselected to provide a space (not shown) between the second substrate 120and the bottom housing 102 when edges of the lateral portions of the tophousing 174 are flush against the edges of the bottom housing 102. Asnoted above, the housing is shown for completeness, and embodiments ofthe invention are not limited to use with a housing. For example, insome embodiments, there may be no screws 140 that are used in assembly170.

FIG. 2 depicts an enlarged view of a portion of the chip carrier 100according to embodiments of the invention. FIG. 2 illustrates thehighlighted portion 150 in FIGS. 1A and 1B to further illustrate bondingof the first substrate 110 to the second substrate 120 using a first UBMstructure 220 and a second UBM structure 230. The first substrate 110has UBM structures 220 attached to a first interconnect structure 240 onthe first substrate 110. The second substrate 120 has UBM structure 230attached to a second interconnect structure 250 on the second substrate120. It should be appreciated that the size of the UBM structures 220and 230 and the size of the interconnect structures 240 and 250 are notdrawn to scale and are shown larger (i.e., exaggerated) for ease ofunderstanding.

The UBM structure 220 includes a first stack of materials and the UBMstructure 230 includes a second stack of materials. The first stack ofmaterials in UBM structure 220 and the second stack of materials in UBMstructure 230 can include multiple layers of materials, particularly twoor more layers. These materials can be thin films. In some embodiments,these materials are composed of metals. For explanation purposes and notlimitation, the UBM structure 220 and UBM structure 230 are depicted ashaving a stack of three layers. The UBM structure 220 can include firstlayer 202, second layer 204, and third layer 206, although fewer or morelayers can be utilized. For example, second layer 204 can be composed ofmultiple layers of materials, such as a multilayered thin filmstructure. The first layer 202 is in direct connect with the firstinterconnect structure 240 and the third layer 206 is in direct contactwith the bump bond 122. The UBM structure 230 can include first layer212, second layer 214, and third layer 216, although fewer or morelayers can be utilized. For example, second layer 214 can be composed ofmultiple layers of materials, such as a multilayered thin filmstructure.

In embodiments of the invention, the layers 202, 204, 206 of UBMstructure 220 can be different from the layers 212, 214, 216 of UBMstructure 230. In other embodiments of the invention, the layers 202,204, 206 of UBM structure 220 can be the same as the layers 212, 214,216 of UBM structure 230. In some embodiments of the invention, some ofthe layers 202, 204, 206 of UBM structure 220 can be different from andsome can be the same as the layers 212, 214, 216 of UBM structure 230.

The first layer 202 acts as an adhesion layer to provide a goodmechanical attachment to the first interconnect structure 240 on thefirst substrate 110. The first layer 212 also acts as an adhesion layerto provide a good mechanical attachment to the second interconnectstructure 250 of the second substrate 120. In some embodiments of theinvention, example materials of the adhesion layer 202 and 212 caninclude Ti, W, Cr, etc.

The second layer 204 in UBM structure 220 and/or the second layer 214 inthe UBM structure 230 is optional. Particularly, the second layer 204 isan intermediate layer in the UBM structure 220 and the second layer 214is an intermediate layer in the UBM structure 230. The second layer 204acts as an adhesion layer to provide a good mechanical attachmentbetween the first layer 202 and the third layer 206. Likewise, thesecond layer 214 acts as an adhesion layer to provide a good mechanicalattachment between the first layer 212 and the third layer 216. In thisway, the second layer is only necessary if the first layers 202 and 212and the third layers 206 and 216 do not adhere well to each otherrespectively. The second layer 204 and/or second layer 214 may also bemultilayered in order to facilitate adhesion between materials used inthe first layers 202 and 212 and in the third layers 206 and 216 thatcannot adhere to each other through a single intermediate materiallayer. In some embodiments of the invention, there may not be a secondlayer 204 and/or second layer 214 since the materials used in the firstlayers 202 and 212 and third layers 206 and 216 might adhere to eachother well. In embodiments of the invention, example materials of theoptional second layer 204 and optional second layer 214 can include: Pd,Pt, Ag, Ru, Os, Rh, Cu, etc.

In both UBM structures 220 and 230, the third layer 206 and the thirdlayer 216 are the bond layer. The third layer 206 bonds to the bump bond122, while the third layer 216 bonds to the bump bond 122 from theopposite side. In some embodiments, the surface of the third layer 206and/or 216 may be wettable to improve the bonding between the thirdlayer 206 and/or 216 and the bump bond 122.

The third layer 206 and third layer 216 need to have the property offorming a good mechanical and electrical connection between the bump 122and the underlying films, where the underlying films are layer 204 orlayer 202 if optional layer 204 is not present in the UBM structure 220and layer 214 or layer 212 if optional layer 214 is not present in theUBM structure 230. In embodiments of the invention, examples of thethird layer 206 and third layer 216 can include Au, Pt, Pd, Ru, Os, Ag,Cu, etc., and alloys of the same. In embodiments of the invention, thethird layer 206 can be comprised of materials that maintain a low ohmicelectrical contact between the solder material 122 at temperatures below100 degrees Kelvin. In embodiments of the invention, the third layer 216can be comprised of materials that maintain a low ohmic electricalcontact between the solder material 122 at temperatures below 100degrees Kelvin. The third layer 206 and third layer 216 create a bondwith the solder bump 122 (from opposite sides). The third layer 206creates a metallic bond with the bump 122, and the strength of the bondcan be partially attributed to diffusion that occurs between thematerials of the bump 122 and third layer 206. The third layer 216creates a metallic bond with the bump 122, and the strength of the bondcan be partially attributed to diffusion that occurs between thematerials of the bump 122 and third layer 216. Diffusion is the movementof atoms between the bonded materials. For example, the layers of theUBM structure 220 (and analogously UBM structure 230) becomesuperconducting because the indium bump 122 above and the Ti film 202below (both of which are superconducting) induce a non-zerosuperconducting order parameter to appear in the normal metal layer 206,thereby causing the entire stack of layers 202, 204, 206 to becomesuperconducting. The same applies by analogy to layers 212, 214, 216 inthe UBM structure 230).

The interconnect structure 240 on the first substrate 110 and theinterconnect structure 250 of the second substrate 120 can take avariety of forms, including, for example, metal on film, damascenemetal, diffusion or any other type of conductive contact area on thefirst substrate and second substrate. The interconnect structure 240and/or interconnect structure 250 may either comprise a physicallycontiguous structure on the surface of their respective substrates 110and 120, or may comprise several structures that are physically separatefrom one another on the surface of their respective substrates 110 and120. Additionally, portions of the interconnect structure 240 and/orinterconnect structure 250 may also be located within their respectivesubstrates 110 and 120. The interconnect structure can be composed of asuperconducting material, such as a superconducting metal or asuperconducting ceramic. In some embodiments, the interconnect structuremay comprise a superconducting material that has a melting point of atleast 700 degrees Celsius such as Nb.

The interconnect structure 240 may serve as an interconnect layer whichelectrically connects electronic circuitry in substrate 110 to theoutside world via electronic connectors 130. The interconnect structure240 can also be an interface that connects to both the electronicconnectors 130 and the interconnect structure 250.

The interconnect structure 240 and possibly layers 202 and/or 204 may beplaced in direct contact with layer 206. When layer 206 is not asuperconducting metal thin film, this physical contact allows for thesuperconducting order parameter in the superconducting films to induce anon-zero order parameter in the normal metal thin film 206, therebycausing it to become superconducting. Similarly, when anon-superconducting metal thin film is used for layer 216, interconnectstructure 250 and possibly layers 212 and/or 214 will similarly causelayer 216 to become superconducting. The length scale of this decay isgoverned by the normal metal coherence length which depends on materialproperties and specifically on cleanliness of the interfaces and thematerial itself, where the material of the third layers 206 and 216 canbe a metallic layer which has both material adhesion properties to theunderlying films (i.e., 204 and 214 or 202 and 212 respectively) and thebump bond 122, plus the ability to be electrically conductive with lowresistance. Typical normal metal materials that can be used here for thethird layers 206 and/or 216 can include: Au, Ag, Ru, Os, Cu, etc. In oneexample, a normal metal film used for the third layer 206 can be asthick as 3 micrometers (μm) or as thin as 10 nanometers (nm), with theactual thickness chosen to provide strong adhesion and to cause theentire stack of layers 202 and 206 (and optionally layer 204) to becomesuperconducting. Similarly, the normal metal film 216 can be as thick as3 micrometers (μm) or as thin as 10 nanometers (nm) to cause the entirestack of layers 212 and 216 (and optionally layer 214) to becomesuperconducting.

Becoming superconducting can also depend on the amount ofcurrent-carrying that is required to pass through interconnect structure240 for UBM structure 220 and/or to pass through interconnect structure250 for UBM structure 230. For very low-current applications, it ispossible to tolerate a thicker layer 206 and/or thicker layer 216. Forhigh current applications, the thickness of each layer 206 and layer 216would be on the low end of the range of 50-100 nm. In embodiments of theinvention, the stack of layer 202/204/206 and stack of layer 212/214/216can each be Ti/Pd/Au. In other examples, the stacks can include othermaterials discussed herein, such as TiSnIn, TiPtTiPd, and WPtAu.

Further, third layer 206 and third layer 216 respectively becomesuperconducting by proximity to the superconducting material of the bumpbond 122. Particularly, having layer 206 and layer 216 become asuperconducting material depends on having a sufficiently thin normalmetal contact layer 206 and layer 216 to allow the superconductivity toextend across its thickness. As such, the thickness of each third layer206 and third layer 216 should be below 3 μm In addition, care should betaken to prepare all interfaces (both above and below layer 206 andlayer 216) to better facilitate superconductivity to occur. Being inproximity can mean that the third layer 206 can become a superconductingmaterial when the third layer 206 comes in (direct) contact (i.e.,physical contact) with a superconducting material, provided that themetallurgy and cleanliness of the material are sufficient to allowdiffusion of the superconducting order parameter into the normal metal,such as when the third layer 206 bonds with the bump bonds 122 made of asuperconducting material. Similarly, being in proximity can mean thatthe third layer 216 becomes a superconducting material when the thirdlayer 216 comes in (direct) contact (i.e., physical contact) with asuperconducting material, such as when the third layer 216 bonds withthe bump bonds 122 made of a superconducting material. As shown in FIG.2, the third layer 206 and third layer 216 of UBM structures 220 and 230are in contact with the bump bonds 122. For example, when the bump bonds122 are indium which is a superconducting material, the third layer 206becomes a superconducting by its proximity to the indium bump bond 122,and likewise the third layer 216 becomes superconducting by itsproximity to the indium bump bond 122. As explained previously, thiseffect is achieved because the physical contact allows for thesuperconducting order parameter in the superconducting films to induce anon-zero order parameter in the normal metal thin films 206 and/or 216,thereby causing it to become superconducting. By having the third layer206 and the third layer 216 become a superconducting material when incontact with, for example, an indium bump bond 122, the connection ofthe respective UBM structures 230 and 240 to the bump bond 122 has zeroresistance or nearly zero resistance.

In some embodiments of the invention, the third layer 206 and/or thethird layer 216 can have a low resistance connection to the bump bond122, where the low resistance connection is less than 1 ohm/contact withthe bump bond 122. Low resistance connection can also be less than 1micro-ohm/contact with the bump bond 122.

Additionally, to create a zero resistance or nearly zero resistanceconnection for signals transmitted back and forth between the UBMstructure 230, the bump bonds 122, and the UBM structure 230 should bethin films. In some embodiments of the invention, the thickness of eachlayer 202, 204, 206 (which can be more or fewer layers as long as layer202 and 206 are present) can be under 3 micrometers (μm) each. In someembodiments of the invention, the thickness of each layer 212, 214, 216(which can be more or fewer layer as long as layer 212 and 216 arepresent) can be under 3 micrometers (μm) each.

The height of the bump bonds 122 for connecting the first and secondsubstrate 110 and 120 together in FIG. 2 is designed to provide apredefined separation distance 260 in the z-axis. In embodiments of theinvention, the separation distance 260 can be about equal to or greaterthan 30 micrometers (μm), about equal to or greater than 60 micrometers(μm), and/or about equal to or greater than 70 micrometers (μm). Beforecompression, examples of heights for the bump bonds 122 in the z-axisinclude about 100 micrometers (μm) or more, about 120 micrometers (μm)or more, etc. As one example, the height of the bump bonds 122 in FIG. 2can be about 100 micrometers (μm) before compression to result in aseparation distance 260 of about 60 micrometers (μm) or more between thefirst and second substrates 110 and 120. The predefined separationdistances 260 discussed herein are technically beneficial because theseparation distance helps to prevent electric fields from couplingbetween the first substrate 110 and the second substrate 120 andaccounts for assembly sensitivity and variations. For example, theseparation distance is sufficient to avoid capacitive coupling betweenelectronic circuitry of substrate 110 and electronic circuitry of secondsubstrate 120. The separation distance is sufficient to avoid/overcome(and be resistant to) issues associated with the surface of the firstsubstrate 110 and the surface of the second substrate 120 not beingpositioned exactly parallel to each other. Thus, even if one substrateis tilted so as to have a surface that is not parallel with respect tothe surface of the other substrate there will be none of the problemsnoted herein.

U.S. Pat. No.: 7,075,171 to Hato describes the use of superconductingsolder bumps bonded directly to superconducting interconnect lines ofNb. Unlike embodiments of the present invention described here, Hatodoes not disclose the unique separation distances and the height ofsolder bump bonds 122 between the first and second substrate 110 and 120discussed herein. In addition, Hato does not describe or teach how onecan bond a superconducting solder bond to a superconducting metalthrough a UBM adhesion structure 220 and 230 as described herein.

WIPO patent application having Publication No.: WO 2017/105524 A1 andInternational Application No.: PCT/US2015/068082 to Mutus describessolder bonding superconducting aluminum wires (transmission lines). Thealuminum transmission lines have a problem when indium soldering makesmaterial contact with it. Thus, Mutus describes forming an intermediatelayer between the indium solder and the aluminum to prevent diffusion ofthe indium solder. Unlike Mutus, the embodiments of the presentinvention do not require a diffusion layer between the (layer 206 orlayer 216) of the UBM structures 220 and 230 and the solder bump 122 andin fact promote diffusion to occur between the indium solder and the UBMstructures 220 and 230.

FIG. 3 depicts an enlarged view of a portion of the chip carrier 100that houses a bump-bonded cryogenic electronic device according toembodiments of the invention. FIG. 3 illustrates the highlighted portion160 in FIGS. 1A and 1B. Similar to FIG. 2, the first substrate 110 hasUBM structure 220 attached to the first interconnect structure 240. Theelectronic connectors 130 are directly attached to the top layer 206 ofthe UBM structure 220. It should be appreciated that the size of the UBMstructure 220 is not drawn to scale and are shown larger for ease ofunderstanding. The bump bonds 122 used to connect the electronicconnectors 130 to the first interconnect 240 on the first substrate 110can be the same as the bump bonds 122 used to connect the first andsecond substrates 110 and 120 together. Similarly, the height of thebump bonds 122 used to connect the electronic connectors 130 may beapproximately the same as the height used to connect the first andsecond substrates 110 and 120 together. In embodiments of the invention,the bump bonds 122 for connecting the electronic connectors 130 to thesubstrate 110 through interconnect structure 240 and for connecting thefirst and second substrates 110 and 120 together are formedsimultaneously. Also, the UBM structures 220 for attaching theelectronic connectors 130 and for attaching the first substrate 110 tothe bump bumps 122 through interconnect structure 240 can be formedsimultaneously.

Additionally, as noted herein, the UBM structure 220 for attaching theelectronic connectors 130 to the first substrate 110 in FIG. 3 can havemore than three layers and/or two layers, such that the third layer 206is attached to the bottom of the microwave connectors 130 and the firstlayer 202 is attached to the first interconnect structure 240 of firstsubstrate 110.

FIG. 4 is a flow chart 400 of a method of forming a bump-bonded device100 according to embodiments of the invention. The process flow includesdepositing metal layers onto the first substrate 110 (which can be thefirst superconducting chip) so as to make the interconnect structure 240at block 402. The metal layers can be formed by sputtering, evaporation,electroplating, direct bond (also referred to a lamination), etc. Themetal layers can be deposited and patterned into the desired circuitryas understood by one skilled in the art.

At block 404, the surface is cleaned. The surface can be cleaned bylaser assisted cleaning, plasma assisted cleaning, sputter cleaning, wetor vapor chemical cleaning, etc.

At block 406, the UBM materials (materials of UBM structure 220) aredeposited on the interconnect structure 240 of the first substrate 110in coordination with the previous or simultaneous cleaning of block 504.This means that some or all of the UBM materials are deposited quicklyafter the clean or in situ within the same cluster tool so that nofurther contamination occurs. Choice of UBM materials (such as, forexample, layers 202, 204, 206) are dictated by diffusion properties andmetallic bonding of various constituent layers. After depositing the UBMmaterials, a photoresist may be patterned over the deposited UBMmaterials in such a way as to define a future pattern of the first UBMstructure 220 through the photoresist patterns that are left remaining.

Alternatively, in block 406, a photoresist is applied and patternedusing standard photoresist processing over the interconnect structure240 of the first substrate 110 in such a way as to define a futurepattern of the first UBM structure 220 through open holes in thephotoresist. Some or all of the UBM materials (materials of UBMstructure 220) are deposited onto the patterned photoresist after thephotoresist patterning has been completed. The UBM can then be formedthrough using a standard lift-off process used to patternmicroelectronics. Choice of UBM materials (such as, for example, layers202, 204, 206) are dictated by diffusion properties and metallic bondingof various constituent layers.

The UBM materials may be deposited through any number of standarddeposition processes such as sputtering, evaporation, electroplating,direct bond (also referred to a lamination), etc. With respect to thedeposition of the UBM materials, there may be no intermediary metallayers, such as no metal layer 204 (which can represent many layers),between the first layer 202 and the last layer 206. Optionally, a secondlayer 204 (or more layers) may be present in between the first and lastlayers 202 and 206.

At block 408, the UBM (e.g., first UBM structure 220) is patterned inorder to restrict the area it occupies during or after the depositionprocess. The UBM (e.g., first UBM structure 220) can be patterned byvarious methods including liftoff, subtractive etch (wet, RIE, etc.,),and direct write using for example ion assisted deposition. Further, thelast layer 206 can be formed using injection molding, but this couldrequire more cleaning. For the other methods of depositing the layer206, in situ cleans can be incorporated and the UBM top metal layer 206can be chosen from a wider group of metals. For example, plating can bedone with top metal layers 206 comprised of Al, Cu, Ru, Ni, and so on.

At block 410, a solder is deposited to create bump bond 122 on the UBMstructures 220 of the first substrate 110. Before depositing the solder,the surface of layer 206 is cleaned as discussed above, for example,using laser assisted cleaning, plasma assisted cleaning, sputtercleaning, wet or vapor chemical cleaning, etc. The bump bond 122 can becreated using standard methods for applying low temperature solder, suchas, for example, mold backfill methods such as plating or injectionmolding, evaporation, and/or sputtering.

At block 412, the bump bonds 122 are cleaned. At this point, the secondsubstrate 120 is not attached on the opposite end of the bump bonds 122.The bump bonds 122 are cleaned as discussed above, for example, usinglaser assisted cleaning, plasma assisted cleaning, sputter cleaning, wetor vapor chemical cleaning, etc. In addition, in a coordinated fashionwith the cleaning of the bump bonds 122, the surface of the third layer216 in UMB structure 230, which is located on interconnect structure 250of the second substrate 120 is similarly cleaned using one of thecleaning techniques described above.

At block 414, shortly after the cleaning step of 412, the bump bonds 122are bonded to second substrate 120 (e.g., which can be a secondsuperconducting chip) through UBM structure 230. In this case, the UBMstructure 230 is called bond metallurgy instead of UBM. Although the toplayer 206 in the first substrate 110 and third layer 216 of the secondsubstrate 120 may be the same in some cases, it is noted that the bondmetallurgy on the second substrate 120 (second chip) can be relaxed. Insuch a case, relaxing the constraint on the bond metal layer 216 (forthe second substrate 120) means it is possible to use flux or reducinggases during the bond procedure. This allows use of oxidizing orotherwise imperfectly clean metallic surfaces for this layer 216 of thesecond substrate 120.

Additionally, it should be noted that the bond is described by thepressing of the second substrate 120 (second chip) onto the bump bonds122 (which are present on the first substrate 110) using a specificrecipe of bond force and temperature as a function of time, as would beunderstood by one skilled in the art.

Also, there are other ways to perform this process. For example, thebumps 122 can initially start on either (chip) just reversing which chipis pressed onto which. That is, the bump bonds 122 can be on the UBMstructure 230 of the second substrate 120 first. Then, the firstsubstrate 110 can be pressed down on top of the second substrate 120. Inaddition, bump bonds 122 can be on both substrates and the bumps arethen pressed on to each other. For example, bumps 122 can be on the UBMstructures 220 and additional bumps 122 can be on the UBM structures230. Accordingly, the first and second substrate 110 and 120 can bepressed together.

FIG. 5 depicts a flow chart 500 of a method of forming a device 100according to embodiments of the invention. At block 502, a firstplurality of thin films (e.g., at least layers 202 and 206 in UBMstructure 220) are formed, and the first plurality of thin films arecharacterized by having a first opposing surface (e.g., on layer 206 inUBM structure 220) and a first connection surface (e.g., on layer 202 inUBM structure 220), where the first connection surface (e.g., film 202in UBM structure 220) is in physical contact with a firstsuperconducting region (interconnect structure 240).

At block 504, a second plurality of thin films (e.g., at least layers212 and 216 in UBM structure 230) are formed, and the second pluralityof thin films are characterized by having a second opposing surface(e.g., on layer 216 in UBM structure 220) and a second connectionsurface (e.g., on layer 212 in UBM structure 230). The first and secondopposing surfaces (of, e.g., layer 206 in UBM structure 220 and layer216 in UBM structure 230) are opposite one another, where the secondconnection surface (e.g., on layer 212 in UBM structure 230) is inphysical contact with a second superconducting region (e.g.,interconnect structure 250).

At block 506, a solder material (e.g., bump bond 122) electricallyconnects the first and second opposing surfaces (e.g., of layer 206 inUBM structure 220 and film 216 in UBM structure 230). The soldermaterial is characterized by maintaining a low ohmic electrical contactbetween the first and second opposing surfaces at temperatures below 100degrees Kelvin, where the first and second superconducting regions arecomprised of materials (e.g., interconnect structure 240 and 250) thathave a melting point of at least 700 degrees Celsius.

The first and second plurality of thin films are electricallyconductive. The first plurality of thin films comprises a stack of filmsin which the stack of films is characterized as having a first opposingfilm (e.g., layer 206 of UBM structure 220) and a first connection film(e.g., layer 202 of UBM structure 220), where the first opposing filmand the first connection film are positioned on opposite ends of thestack of films.

The first opposing film (e.g., layer 206 of UBM structure 220) is inphysical contact with the solder material (e.g., bump bond 122) and thefirst connection film (e.g., layer 202 of UBM structure 220) is inphysical contact with the first superconducting region (e.g.,interconnect structure 240). The first opposing film is comprised of afirst material and the first connection film is comprised of a secondmaterial, where the first and second materials are different from eachother. The first and second materials are metals.

At least one intermediate film (e.g., layer 204 of UBM structure 220) ispositioned between the first opposing film (e.g., layer 206 of UBMstructure 220) and the first connection film (e.g., layer 202 of UBMstructure 220). The at least one intermediate film (e.g., layer 204 ofUBM structure 220) facilitates a mechanical bond between the firstopposing film (e.g., layer 206 of UBM structure 220) and the firstconnection film (e.g., layer 202 of UBM structure 220). The at least oneintermediate film is characterized as being a different material fromthe first opposing film and the first connection film. The at least oneintermediate film is a metal. The first superconducting region (e.g.,interconnect structure 240) is in contact with a first substrate (e.g.,substrate 110) and the second superconducting region (e.g., interconnectstructure 250) is in contact with a second substrate (e.g., substrate120).

The solder material (e.g., bump bonds 122) has a height that causes aseparation distance (e.g., separation distance 260) between the firstand second substrates (e.g., substrates 110 and 120). The separationdistance (e.g. separation distance 260) between the first and secondsubstrates is selected from the group consisting of the separationdistance of about or greater than 50 micrometers (μm), the separationdistance of about or greater than 60 micrometers (μ), and the separationdistance of about or greater than 70 micrometers (μm).

FIG. 6 depicts a system 600 in which the device 100 has been placed intoa cooling system 602 according to embodiments of the invention. Thesystem 600 shows that one or more input and output lines 606 areconnected to the chip carrier 100 that houses the bump-bonded cryogenicelectronic device structures in the cooling system 602. The coolingsystem 602 can be a cryogenic cooling device, dilution refrigerator,etc. The chip carrier 100 that houses the bump-bonded cryogenicelectronic device is cooled to superconducting temperatures (lowtemperatures), such as below 100 millikelvin (mK), at about 10-100 mK,and/or about 4 K.

Thus, it can be seen from the foregoing detailed description andaccompanying illustrations that embodiments of the present inventionprovide systems, methodologies and resulting chip carrier that housesthe bump-bonded cryogenic electronic device structures configured toexecute the direct transfer of electronic signals into and out of one ormore circuits in a manner that eliminates the need for intermediaryconnection mechanisms such as PCBs, wire bond connections, and the like.In embodiments of the invention, a merged fabrication process is used toform two different types of electrical connections on a first substrate.In embodiments of the invention, the two different types of electricalconnections includes electronic connectors (e.g., microwave connectors)and bump bonds, and the merged fabrication process attaches the twodifferent types of connectors through an interconnect structure.

As previously noted herein, for the sake of brevity, conventionaltechniques related to circuits may or may not have been described indetail. By way of background, however, a more general description of theelectrical device fabrication processes that can be utilized inimplementing embodiments of the present invention will now be provided.Although specific fabrication operations used in implementingembodiments of the present invention may or may not be individuallyknown, the disclosed combination of operations and/or resultingstructures of the embodiments of the present invention are unique. Thus,the unique combination of the operations described in connection withthe fabrication of a coupler system according to embodiments of thepresent invention utilize a variety of individually known physical andchemical processes performed on a substrate.

Fundamental to fabrication processes can be lithography, i.e., theformation of three-dimensional relief images or patterns on thesubstrate for subsequent transfer of the pattern to the substrate. Inlithography, the patterns are a light sensitive polymer called aphotoresist. To build the complex structures that make up a transistorand the many wires that connect the millions of transistors of acircuit, lithography and etch pattern transfer steps are repeatedmultiple times. Each pattern being printed on the substrate is alignedto the previously formed patterns and slowly the conductors, insulatorsand selectively doped regions are built up to form the final device.

In some embodiments, various functions or acts can take place at a givenlocation and/or in connection with the operation of one or moreapparatuses or systems. In some embodiments, a portion of a givenfunction or act can be performed at a first device or location, and theremainder of the function or act can be performed at one or moreadditional devices or locations.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescribed embodiments of the present invention has been presented forpurposes of illustration and description, but is not intended to beexhaustive or limited to the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiments were chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

The term “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment or design described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments or designs. The terms “at least one”and “one or more” can include any integer number greater than or equalto one, i.e. one, two, three, four, etc. The terms “a plurality” caninclude any integer number greater than or equal to two, i.e. two,three, four, five, etc. The term “connection” can include both anindirect “connection” and a direct “connection.”

The flowchart and block diagrams in the figures illustrate thefunctionality and operation of possible implementations of systems andmethods according to various embodiments of the present invention. Insome alternative implementations, the functions noted in the block canoccur out of the order noted in the figures. For example, two blocksshown in succession can, in fact, be executed substantiallyconcurrently, or the blocks can sometimes be executed in the reverseorder, depending upon the functionality involved. The actions can beperformed in a differing order or actions can be added, deleted ormodified. Also, the term “coupled” describes having a signal pathbetween two elements and does not imply a direct connection between theelements with no intervening elements/connections therebetween. All ofthese variations are considered a part of the invention.

The terms “about,” “substantially” and equivalents thereof are intendedto include the degree of error associated with measurement of theparticular quantity based upon the equipment available at the time offiling the application. For example, “about,” “substantially” andequivalents thereof can include a range of ±8% or 5%, or 2% of a givenvalue.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentinvention. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,element components, and/or groups thereof.

While the present invention has been described in detail in connectionwith only a limited number of embodiments, it should be readilyunderstood that the present invention is not limited to such disclosedembodiments. Rather, the present invention can be modified toincorporate any number of variations, alterations, substitutions orequivalent arrangements not heretofore described, but which arecommensurate with the spirit and scope of the present invention.Additionally, while various embodiments of the present invention havebeen described, it is to be understood that aspects of the presentinvention can include only some of the described embodiments.Accordingly, the present invention is not to be seen as limited by theforegoing description, but is only limited by the scope of the appendedclaims.

What is claimed is:
 1. A device comprising: a first plurality of thinfilms, the first plurality of thin films characterized by having a firstopposing surface and a first connection surface, wherein the firstconnection surface is in physical contact with a first superconductingregion; a second plurality of thin films, the second plurality of thinfilms characterized by having a second opposing surface and a secondconnection surface, the first and second opposing surfaces beingopposite one another, wherein the second connection surface is inphysical contact with a second superconducting region; and a soldermaterial electrically connecting the first and second opposing surfaces,the solder material characterized by maintaining a low ohmic electricalcontact between the first and second opposing surfaces at temperaturesbelow 100 degrees Kelvin, wherein the first and second superconductingregions are comprised of materials that have a melting point of at least700 degrees Celsius.
 2. The device of claim 1, wherein the first andsecond plurality of thin films are electrically conductive.
 3. Thedevice of claim 1, wherein the first plurality of thin films comprises astack of films, the stack of films characterized as having a firstopposing film and a first connection film, the first opposing film andthe first connection film positioned on opposite ends of the stack offilms.
 4. The device of claim 3, wherein the first opposing film is inphysical contact with the solder material and the first connection filmis in physical contact with the first superconducting region.
 5. Thedevice of claim 3, wherein the first opposing film is comprised of afirst material and the first connection film is comprised of a secondmaterial, wherein the first and second materials are different from eachother.
 6. The device of claim 5, wherein the first and second materialsare metals.
 7. The device of claim 5, wherein at least one intermediatefilm is positioned between the first opposing film and the firstconnection film, the at least one intermediate film facilitating amechanical bond between the first opposing film and the first connectionfilm, the at least on intermediate film characterized as being adifferent material from the first opposing film and the first connectionfilm.
 8. The device of claim 7, wherein the at least one intermediatefilm is a metal.
 9. The device of claim 1, wherein the firstsuperconducting region is in contact with a first substrate and thesecond superconducting region is in contact with a second substrate. 10.The device of claim 7, wherein the solder material has a height thatcauses a separation distance between the first and second substrates,wherein the separation distance between the first and second substratesis selected from the group consisting of the separation distance ofabout or greater than 50 micrometers (μm), the separation distance ofabout or greater than 60 micrometers (μm), and the separation distanceof about or greater than 70 micrometers (μm).
 11. A device comprising: afirst plurality of thin films in physical contact with a first substrateat a first superconducting region, the first plurality of thin filmscharacterized by having a first opposing surface and a first connectionsurface, wherein the first connection surface is in the physical contactwith the first superconducting region; a second plurality of thin filmsin physical contact with a second substrate at a second superconductingregion, the second plurality of thin films characterized by having asecond opposing surface and a second connection surface, the first andsecond opposing surfaces being opposite one another, wherein the secondconnection surface is in the physical contact with the secondsuperconducting region; and a solder material electrically connectingthe first and second opposing surfaces, the solder materialcharacterized by maintaining a low ohmic electrical contact between thefirst and second opposing surfaces at temperatures below 100 degreesKelvin, wherein the first and second superconducting regions arecomprised of materials that have a melting point of at least 700 degreesCelsius.
 12. The device of claim 11, wherein the first and secondplurality of thin films are electrically conductive.
 13. The device ofclaim 1, wherein the first plurality of thin films comprises a stack offilms, the stack of films characterized as having a first opposing filmand a first connection film, the first opposing film and the firstconnection film positioned on opposite ends of the stack of films. 14.The device of claim 13, wherein the first opposing film is in physicalcontact with the solder material and the first connection film is inphysical contact with the first superconducting region.
 15. The deviceof claim 13, wherein the first opposing film is comprised of a firstmaterial and the first connection film is comprised of a secondmaterial, wherein the first and second materials are different from eachother.
 16. The device of claim 15, wherein the first and secondmaterials are metals.
 17. The device of claim 15, wherein at least oneintermediate film is positioned between the first opposing film and thefirst connection film, the at least one intermediate film facilitating amechanical bond between the first opposing film and the first connectionfilm, the at least on intermediate film characterized as being adifferent material from the first opposing film and the first connectionfilm.
 18. The device of claim 17, wherein the at least one intermediatefilm is a metal.
 19. A system comprising: a cooling system; a device inthe cooling system, the device comprising: a first plurality of thinfilms, the first plurality of thin films characterized by having a firstopposing surface and a first connection surface, wherein the firstconnection surface is in physical contact with a first superconductingregion; a second plurality of thin films, the second plurality of thinfilms characterized by having a second opposing surface and a secondconnection surface, the first and second opposing surfaces beingopposite one another, wherein the second connection surface is inphysical contact with a second superconducting region; and a soldermaterial electrically connecting the first and second opposing surfaces,the solder material characterized by maintaining a low ohmic electricalcontact between the first and second opposing surfaces at temperaturesbelow 100 degrees Kelvin, wherein the first and second superconductingregions are comprised of materials that have a melting point of at least700 degrees Celsius.
 20. The system of claim 19, wherein the first andsecond plurality of thin films are electrically conductive.
 21. Thesystem of claim 19, wherein the first plurality of thin films comprisesa stack of films, the stack of films characterized as having a firstopposing film and a first connection film, the first opposing film andthe first connection film positioned on opposite ends of the stack offilms.
 22. The system of claim 21, wherein the first opposing film is inphysical contact with the solder material and the first connection filmis in physical contact with the first superconducting region.
 23. Amethod of configuring a device, the method comprising: forming a firstplurality of thin films, the first plurality of thin films characterizedby having a first opposing surface and a first connection surface,wherein the first connection surface is in physical contact with a firstsuperconducting region; forming second plurality of thin films, thesecond plurality of thin films characterized by having a second opposingsurface and a second connection surface, the first and second opposingsurfaces being opposite one another, wherein the second connectionsurface is in physical contact with a second superconducting region; andjoining the first and second opposing surfaces with a solder materialsuch that the solder material electrically connects the first and secondopposing surfaces, the solder material characterized by maintaining alow ohmic electrical contact between the first and second opposingsurfaces at temperatures below 100 degrees Kelvin, wherein the first andsecond superconducting regions are comprised of materials that have amelting point of at least 700 degrees Celsius.
 24. The method of claim23, wherein the first and second plurality of thin films areelectrically conductive.
 25. The method of claim 23, wherein the firstplurality of thin films comprises a stack of films, the stack of filmscharacterized as having a first opposing film and a first connectionfilm, the first opposing film and the first connection film positionedon opposite ends of the stack of films.